1. Field of the Invention
The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery.
2. Description of the Related Art
A non-aqueous electrolyte secondary battery used as a secondary battery for electric vehicles and capable of charging and discharging, is desired to have a high energy density (capacity density) so as to be able to increase a travel distance thereof. Therefore, recently, consideration is given on using FeF3 as a positive electrode active material of the non-aqueous electrolyte secondary battery. The positive electrode active material forms a positive electrode material by being mixed with a conductive auxiliary, a binder and the like.
FeF3 has a high theoretical energy density (reversible capacity), and for example a non-aqueous electrolyte secondary battery using FeF3 as a positive electrode active material and Li as a negative electrode active material is said to have a theoretical energy density of approximately 240 mAh/g (for example, refer to Japanese Patent Application Laid-Open No. 2008-130265).
On the other hand, when the non-aqueous electrolyte secondary battery is used as the secondary battery for electric vehicles, it is desired to be superior in charge-discharge characteristics in a region which involves high current density from receiving high load, such as during high-speed traveling or during hill-climbing (hereinafter sometimes referred to as a high-load characteristics). The charge-discharge characteristics is, for example, indicated by a capacity density when discharge is performed from a predetermined initial potential to a predetermined potential.
However, the positive electrode active material comprising FeF3 has an inconvenience that, when the same is used in the non-aqueous electrolyte secondary battery, sufficient charge-discharge characteristics cannot be obtained in the region which involves high current density.